Reconstructing Dark Matter Density with e^+e^- Linear Collider in Focus-Point Supersymmetry

It has been known that, in the focus point scenario of supersymmetry, the thermal relic of the lightest superparticle (LSP) is known to be a good candidate of the cold dark matter. Assuming that the LSP in the focus-point scenario be the cold dark matter, we address a question how and how well the relic density of the LSP can be determined once the superparticles are found at future e^+e^- linear collider. We will see that the determinations of the mass of the LSP as well as those of the Higgsino-like chargino and neutralinos, which will be possible by a study of the decay kinematics of the chargino or by threshold scan, will give us important information to theoretically reconstruct the relic density. Even if the Higgsino-like superparticles and the LSP are the only superparticles which are kinematically accessible, relic density of the LSP may be calculated with the accuracy of factor \sim 2; by adopting a mild theoretical assumption or by determining the masses of the Wino-like superparticles, uncertaintiy can be reduced to \sim 10 % or smaller.